Enchant creature card in a graveyard.
When Animate dead enters the battlefield, if it's on the battlefield, it loses "enchant creature card in a graveyard" and gets "enchant creature put onto the battlefield with Animate Dead. Return enchanted creature card to the battlefield under your control and attach Animate Dead to it. When Animate Dead leaves the battlefield, that creature's controller sacrifices it.
Enchanted creature gets -1/-0.

Haste
When Avarax enters the battlefield, you may search your library for a card named Avarax, reveal it, and put it into your hand. If you do, shuffle your library.
1R: Avarax gets +1/+0 until end of turn.

Flying
Vanishing 3 (This creature enters the battlefield with three time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
When Aven Riftwatcher enters the battlefield or leaves the battlefield, you gain 2 life.